Entity Relationship Diagram Legend

A black circle leading to an open diamond indicates a one-to-many relationship between the primary key of the first table and the foreign key of the second table. For an example of this look at the figure for the Registry Tables Group. Extension is a primary key of the Extension table and a foreign key of the Verb table. One Extension can therefore can be registered to have several Verbs, but a particular Verb can only be associated to one Extension.